Method of handling and cooling foundry sand



United States Patent Ofice 3,461,941 Patented Aug. 19,, 1969 3,461,941 METHOD OF HANDLING AND COOLING FOUNDRY SAND Joseph S. Schumacher, 7256 Concord Ridge Drive, Cincinnati, Ohio 45230 No Drawing. Filed Mar. 19, 1968, Ser. No. 714,339 Int. Cl. 1322c 5/18, 25/00; B22d 47/02 US. Cl. 164-5 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method for handling foundry sand. More particularly, it relates to a method for handling foundry sand wherein the temperature of the sand is cooled to a desired temperature after it has been used.

In a recent article entitled Survey of Methods to Cool Hot Sand written by A. J. Filipovitch, and appearing at page 92 in volume 95, No. 10, of the October 1967 issue of Foundry magazine, a survey of the methods used by 211 foundries to cool foundry sand is presented. The author reports that the most frequently used methods for cooling foundry sands include costly apparatus such as mullers, belt aerators, rotary screens, fluidizing units, perforated cooling conveyors, cooling elevators and cooling tables. He states that all of the methods rely upon the use of water to lower the temperature of the hot, used sand to about 170 F. and then on air cooling to further reduce the temperature. The optimum temperature to which the sand must be cooled to is about room temperature.

If foundry sand which has been used is not cooled before it is reused, several problems arise. It is pointed out in the article referred to previously that hot sand is very unstable and its properties change as its moisture evaporates. This moisture also causes poor pattern draws resulting in inferior casting quality. It is also known that variations in moisture, even though they appear inconsequential, can cause radical changes in compressive strength, permeability and flowability. These changes can lead to poor finish, defective castings and increased scrap. If too much moisture is added, the sand tends to agglomerate. Another problem that is present is that when hot sand is conveyed, it does not flow very Well and tends to pack and agglomerate in the equipment, tanks, conveyors and elevators. The constant and rapid loss of moisture by evaporation as the sand cools creates in a quantity of sand a condition of dryness on the surface to wet in the center. Uniformity of properties is a condition to quality. It does not exist in hot sand.

An important object of my invention is to provide a method for cooling foundry sand to approximately room temperature without the need for using expensive and complicated cooling equipment. Another important objective of my invention is to provide a method for cooling foundry sand which does not depend upon air or water as the cooling medium. A still further objective of this invention is to provide a foundry sand handling system wherein the composition of the foundry sand can be easily controlled and the compositional variations are minimized.

In the casting of metals into sand molds, the amount of sand used to form a mold is usually expressed as a function of the amount of metal to be poured into it. This relationship is called the sand to metal ratio. For example, sufiicient sand can be used for the mold to give a sand to metal ratio of from 3 to 1 to 20 to 1. While these ratios are frequently used, others are oftentimes used too. A common ratio used is a ratio of about 6 to 1. That is, a mold is formed which consists of 6 pounds of sand for each pound of metal to be cast.

Foundry sand is, of course, not sand alone but contains additional constituents such as clays, carbons and/or other additives. Carbons in common use are, powdered coal, coal tar, pitch, asphalt, graphite and coke. Other additives can be added such as celluloses, cereal binders, etc. After one or more molding operations, new sand, clays and carbons can be added to the used sand to replace the portion of the original sand which has been made unusable. The following is a typical table which shows the amount of additives which usually must be added after the batch of sand has been used. This table is for ferrous metals other than steel. Other data for nonferrous metals, steel and ductile metals is known to those in the foundry industry.

TABLE I.SUGGESTED ADDIIIVE REQUIREMENTS PER MULLER LOAD OF 2,000 POUNDS Clay Ratio sand/metal bentonite (lbs.) Carbons (lbs.) New sand (lbs.)

As it can be seen from this table, it requires about 34.8 pounds of new clay and additives plus pounds of new sand to reconstitute the molding sand for reuse at a sand to metal ratio of 3 to 1. However, at a ratio of 20 to 1 it requires only 5.2 pounds of new clay and additives, plus 15 pounds of new sand to reconstitute it at this ratio.

I have discovered that if one desires to operate a sand system at a normal sand to metal ratio of about 4 to l to 6 to 1 that conventional cooling methods can be eliminated if a batch of foundry sand is mixed so as to provide a 20 to 1 ratio, the molds are made, for example, on a 4 to l to 6 to 1 ratio, and if immediately after the molds are used and broken up, the remaining unused cool portion of the mixed sand is mixed with the hot used sand, By mixing the unused sand with the used sand, the temperature of the combination of sand is lowered so that a portion of the batch can be reused immediately after it has been remulled without further cooling. No other cooling step is needed. Moreover, sand used in this manner is easy to reconstitute because the amount of additives lost per molding cycle expressed as a percent of the total batch is very small. It can be seen, therefore, that my invention provides a novel method of cooling foundry sand While at the same time it provides a method for controlling the composition of the foundry sand and for minimizing variations in composition.

I have found that it is generally desirable to cool the used sand as close to ambient temperature as possible after the molds are shaken out and prior to the mulling and reconstituting of the sand. While ambient temperature is preferred, sand at a temperature of F. can be used. However, it is desirable to cool the sand to below 120 F. to obtain the best mixing results. Most clays are difiicult to wet and plasticize when the temperature is over 120 F. If sands are prepared at 120 F. then drying out will rapidly occur due to evaporation till ambient temperature'is reached. Moisture losses change the properties of the molding sand. A consistent molding media is desired for best results. Therefore, I have found that the most efficient mixing is achieved when the sand is at ambient temperature. The amount of sand which must be added after shakeout in order to obtain a mixture of used and unused sand at a particular temperature is, of course, dependent upon the temperature of and the amounts of the used and unused sands. I have found that the approximate amount of unused sand which must be added can be calculated in the following way.

An approximate estimation of the temperature of the sand at shakeout can be made if it is assumed that all the heat evolved from the hot metal is transferred to the sand. The temperature of the metal in an average pouring for iron is about 2600 F. The heat evolved can be calculated from the following formula H=cp (t60) where cp=mean specific heat of pure iron at 2600 F., t=shakeout temperature, and 60=standard ambient temperature. No heat of solidification has been included because of the different metals which might be used. The following table shows the heat evolved at the indicated shakeout temperature when the pouring temperature is 2600 F.

TABLE II Heat evolvedB.t.u. 1 1b. of metal Shakeout temp. of in metal casting:

These results can be plotted on a graph so that the intermediate values can be easily obtained.

Knowing the heat evolved from the metal and assuming that all of this heat is transferred to the sand then the temperature of the sand at various shakeout temperatures can be calculated. The formula that should be used is H:cp sand weight per pound of iron (t-60) where H is the heat evolved from the iron, cp is the heat is SiO for t-60, and t=sand temperature at shakeout. The following tables show the temperature of the sand at various metal shakeout temperatures.

TABLE III-20 to 1 Sand to Metal Ratio Casting shakeout temp, F.: Sand temperature, F

TABLE IV.- to 1 Sand to Metal aRtio Casting shakeout temp, F.: Sand temperature, F.

TABLE V.4 to 1 Sand to Metal aRtio Casting shakeout temp., F.: Sand temperature, F.

Again it was assumed that the pouring temperature of the metal was 2600 F. The above temperatures can be plotted so that intermediate temperatures can be determined quickly. The above calculated sand temperatures assume that there is no moisture in the sand. However, in practice there is usually between 3 to 5% of water in the sand. The evaporation of this moisture will cool the sand still further. For example, at a 10 to 1 sand to metal ratio the sand will be cooled about 53 for each 1% of moisture evaporated. In most foundries the shakeout temperature is between 1000 F. and 1300 F. Therefore, in order to have sand at not more than 120 F. as it goes into the muller, the sand to metal ratio at this point must be between 10 to 1 and 20 to l. A 10 to 1 mixture will provide this temperature because about 3% of moisture has been evaporated.

The amount of sand actually used to form the mold can be any ratio but common values are a sand to metal ratio of 4 to l to about 6 to 1.

Conventional foundries usually have a muller, a sand storage bin, a molding machine and some means for breaking up the used sand molds and separating the castings. Such a conventional sand system with the conveyors, muller, etc. is shown at pages 9 and 10 of the aforementioned foundry magazine. In my system any number of the various kinds of batch or continuous mullers, molding machines and shakeout mechanisms can be used. Such devices are well known to those in the art and the use of any particular one forms no basis of invention of this application and is not required in my process.

The following is an example of how my process has been successfully practiced at a foundry where expensive equipment had previously been used to cool its foundry sand.

The muller used at the foundry was a continuous muller, that is, a continuous flow of sand was introduced into the muller and a continuous flow of mulled sand was discharged from the muller. The approximate composition of sand used was 89% silica, 6% clay, 5.3% carbons and 4% water. Periodic additions of clays, carbons and new sand, calculated according to the figures shown in Table I were made to the sand at the muller during the casting cycle. A large amount of sand was prepared. However, the molds were made on a 4 to 1 sand to metal ratio. The metal cast was a malleable iron having an approximate composition of 3.5% total carbon and 0.6% Si. The sand which was not used to form the molds was conveyed to a storage tank. After the metal was cast, the casings and molds were conveyed to a shakeout station and the molds broken. Immediately after the castings were separated from the broken molds at the shakeout station, about 16 parts of cool sand at ambient temperature from the storage tank were added to the hot used sand. The temperature of the used sand prior to the addition of the unused sand was over 350 F. By the time the mixture of hot used sand and cool unused sand had been transported by a conventional conveyor to a second storage bin, a distance of approximately 200 feet, the temperature of the batch was approximately 100 F. After this, the sand was conveyed to the muller. After the mulling process, the temperature of the sand was approximately 90 F. No additional cooling of the sand was provided. It was then conveyed to the first storage tank. After using this process for several weeks, it was apparent that the quality of the molds and of the finished castings was greatly improved over the process previously practiced which included conventional sand cooling apparatus. Moreover, it was found that it was much easier to control the composition of the sand and there was much less variation in the composition. Additionally it was found that the sand was much easier to handle because its flowability was improved. Another unexpected result was that air pollution was drastically reduced. It is believed that expensive air cleaning equipment will also be eliminated by using my process.

The above example is, of course, only one example of how my process can be practiced. Those skilled in the art will immediately recognize that the inventive concept of my invention is the use of a large quantity of relatively cool sand to cool a much smaller quantity of hot used sand.

Having thus described my invention, I claim: 1. A foundry process comprising preparing a batch of foundry sand having a weight of at least ten times the weight of the metal to be cast,

forming molds from a minor portion of said batch of sand, said molds each having a weight of from 3 to 6 times the weight of the material to be cast,

retaining the major portion of foundry sand for the later cooling of said minor portion,

casting metal in the molds,

breaking said molds and separating the metal from said used sand, and

cooling said used sand by mixing with it said major portion of sand whereby the mixture has a temperature of below 120 F.

2. The foundry process of claim 1 wherein the molds have a Weight of about 4 times the weight of the material to be cast and the weight of the major portion is at least 16 times the weight of the metal to be cast.

3. The process of claim 1 wherein minor amounts of additives are added to the used sand.

4. The process of claim 1 wherein the temperature of said major portion is less than 90 F.

5. A foundry process which comprises mulling used sand to provide a quantity of sand of at least as great as times the weight of the metal to be cast, said used sand derived from a later step in the process,

forming molds from a minor portion of themulled mixture, said molds each having a weight of at least 3 times the weight of the material to be cast,

retaining the major portion of foundry sand for the later cooling of said minor portion,

casting metal in the molds,

separating the metal from said molds,

cooling said used sand by mixing it with said major portion of sand whereby the mixture has a temperature of below 120 F., and

retaining the major portion of foundry sand for the later aforesaid mulling step.

6. The foundry process of claim 5 wherein the molds have a weight of about 4 times the weight of the material to be cast and the weight of the major portion is at least 16 times the weight of the metal cast.

7. The foundry process of claim 6 wherein minor amounts of additives are added to the mixture of the major and minor portions of sand.

8. The foundry process of claim 6 wherein the temperature of said major portion is less than F.

References Cited UNITED STATES PATENTS 8/1949 Connolly 1645 X 5/1950 Chamberlin 1645 US. Cl. X.R.

UNITED STATES PATENT OFFIVCE CERTIFICATE OF CORRECTION Patent No. 3 4b] 94] Datedv A 12 1 2&2

Inventor(s) Joseph S. Schumacher It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, Table 1, column entitled "New sand (lbs.)" should read New sand lbs. 2

15.0 line 51, after "sand", should be line 28, "in" should be --the--. line 46, "casings" should be --castings-- line 22, "Claim 1" should be --Claim 2--; line 24, "Claim should be --Claim 2-- Column line 5, "it with" should be --with it--; lines 8 z 9, "retaining the major portion of foundry sand for the late aforesaid mulling step." should be --returning the minor and major portions of sand to the aforesaid mulling step.--

Column Column Column Column SIGNED KND SEALED JUN161970 (SEAL) Afloat:

Edwm-dlLFlflnhqIr. WILLIAM L i Atteszi ()ffi Comissioner of Paton FORM PO-IOSO (IO-69) 

